Coupling circuit



H. M. EVJEN ETAL COUPLING CIRCUIT Filed April 25, 1942 F eb. 29, 1944.

, tion.

Patented Feb. 29,/1944 COUPLING CIRCUIT Haakon M. Evien and William Bradley Lewis, Houston, Tex., assignors to Nordel Corporation, Houston, Tex., a corporationof Delaware Application April'23, 1942, Serial No. 440,264

` (c1. irs-isz) claims This invention relatesl to a novel and improved coupling' circuit for coupling independent electric circuits and more particularly to a coupling circuit deriving energy from a circuit carrying either dir ect current or 'low frequency alternating current and producing a secondary direct current that is directly proportional to the amplitudeof said rst current.

An object is to'provide a novel and improved coupling circuit of the above type. in which no direct current path is established between the coupled circuits. c

Another object of the invention is to provide a novel and improved circuit of the above type which is adapted for use with a circuit carrying direct current orcarryins alternating current of such low frequency that ordinary transformer couplingisnot feasible.

Y Other objects and advantages -will be apparent `asthe nature of the invention is more fully disclosed. v

The present coupling circuit has a wide application in the field. of precision electrical measurements. A particular embodiment as applied to a seophysical prospecting system is set forth herein for purposes of illustration only. 4

Although the novel features which are believed to be characteristic of this invention are pointed out more .particularly in the claims appended hereto, the invention itself may be better understood by referring to 'the following descrip-.

tion, taken in connection with the accompanying drawings, inwhlch a specific embodiment thereof has been set forth for the purposes of illustra- Inthe'drawin:

'Fis'. 1 is a schematic embodiment of the invention;

Fig. 2 is a schematic diagram illustrating another embodiment of the invention; and

Fig. 3 is a schematic diagram illustrating the invention applied to an electrical geophysical prospecting system.

circuit. 'I'he alternating secondary voltage is rectiiied to produce a unidirectional current which is directly proportional to the current flowing in said ilrst circuit.

In the embodiment shownin Fig. 1 a magnetic. core 2 is provided with a primaryv coil 3 and a. secondary coil I and with a segment 5 of mag-i netic material which is mounted for rotation on a shaft `6 driven; by a motor l. The segment 5- completes the magnetic circuit of the core 2 and. forms therewith gaps 8 which are small with the. segment V5 in the position shown but increase. in size when the segment is .rotatedinto a position at right angles to that shown,v thereby periodi-- cally varying the reluctance of the magnetic circuit. l

The primary coil 2 is shown as connected to a pair of input terminals lIl and Il. 'I'he secondary coil I is connected by lines I4 and I 5 to an impedance network I8 and thence by lines 2| and 22 to a rectier 23. The D. C. output of the 'rectifier 23 is connected to a resistance 24 having adjustable taps 25 and 26. Ihe impedance network IB is so designed that the amplitude of the output current is substantially independent of variations in frequency, so that the direct curpiitude of the primary current.

diagram illustrating one e In accordance with the present invention the frequency corresponding to the frequency of ux variation and having an amplitude corresponding to the amplitude oi' the current in the ilrst In the embodiment shown the network I6 comprises a resistance i1 and a condenser I8 con-- nected in series between the lines Il and l5. If the characteristics of the secondary 4 are such that the current increases with frequency, i. e., with increase in speed of rotation of the segment 5 which correspondingly increases the voltage induced in the secondary l, the eilect is counteracted by the shunt condenser I8 which has a lower impedance at higher frequencies and thus by-passes a greater portion of the total current.

The values of the resistance I1 and the condenser I8 may be so chosen with respect to the char- Aput characteristics.-

The rectier 23 is shown as a vfull Wave rectifier comprising a pair of oxide rectiilers I9. connected across a resistor 20. The` output resistor current or an alternating current of low frequency passing through the primary coil 3 produces a flux in the magnetic circuit of the core 2 and the segment 5. Y |The value of the fiux threading the secondary coil 4 varies periodically at a frequency double the frequency of rotation of the segment 5. An alternating current of a controlled frequency is thus produced in the secondary coil 4 having an amplitude proportional to the current flowing in the primary 3 and having a frequency which is determined by the speed of rotation of the segment 5. This alternating current, is then passed through the impedance network l5, is rectified in the rectier 23 and is passed as direct Current through the resistance 24 to produce therein a potential drop which is directly proportional to the current flowing in the primary coil 3.

Fig. 2 shows another arrangement for obtaining a varying iiux in the secondary coil which may be substituted for the magnetic core 2 of Fig. l.- In this figure the input terminals i and it are connected by lines 13 and 1| and brushes i2 and 13 to slip rings 14 and 15 respectively. These slip rings 14 and 15 are connected to a rotating coil 3' forming the primary of a transformer 11. The secondary 4' of the transformer 11 is connected to lines I4 and i5 which are con- ;cteld to the filter i6 and rectiiier 23 as in In this embodiment the primary current is passed through the coil 3', which is rotated by any. suitable means and at a predetermined speed. The ilux produced by the coil 3'may be constant or substantially constant in the case of direct current and in the case of low frequencyalternating current will be reversed at a corresponding rate. This, however, is low as compared with the speed of rotation of the coil 3. The flux threading the coil 4' will accordingly have an average value which is determined by the value of the current flowing in the coil 3', but will be reversed at a frequency corresponding to the Speed of rotation of the coil 3. In this way an alternating current is produced in the coil 4 havlng a value dependent upon thevalue of the primary current and having a frequency which may be varied and controlled as desired.

The application of the above described coupling circuit to a system of geophysical exploration of the general type disclosed in the copending application of Knute Evien, Ser. 310,109 (now Patent 2,294,395), is shown in'Fig. 3. In this ligure the coupling circuit of Fig. 1 or Fig. 2 is indicated by the rectangle A. Referring to Fig. 3, a source 35 of direct current is connected by lines 36 and 31 to a reversing switch 3l having reversing contacts 4c and 4 i. An ammeter 42 is shown as connected in series with the lead 31. The reversing contact 45 of the switch 39 is connected by a lead 43 to a ground electrode d4. The reversing contact 4i is connected by a lead c5 to the input terminal E0 of the coupling circuit A. The input terminal i! is connected by a lead 4t to a second ground electrode t1.

` The output terminals 21l and 28 of the coupling circuit A are connected by lines 50 and 5i to a reversing switch 52 having reversing contacts 53 and 54. A direct current galvanometer 55 is shown asL connected in series. with the lead 50. The reversing contact 53 of the switch 52 is connected by a line 55 to an earth potential pickup electrode 51. The other reversing contact 54 is connected by a line 58 to the adjustable contact 59 of a potentiometer 60 across which a. battery 6i is connected. The midpoint of the battery 6| is connected by a lead 52 to a second earth potential pick-up electrode E3. l

The reversing switches 3l and 52 may be of any suitable type, for example, of the type shown l5 in the copending application of Haakon M. Evjen,

Ser. 432,176 (now Patent 2,314,874) and are operated inv synchronism.

In the operation of this system a current is passed through the earth between the electrodes 44 and 41 having a definite value and frequency. the value being dependent upon the source 35 and the frequency being dependent upon the frequency of operation of the reversing switch 3l. The potential pick-up electrodes 51 and 63 are located at spaced points adjacent the earths surface within the eld of inuence of the earth current produced by the earth current flowing between the current electrodes 44 and 41. This current is reversed at a frequency corresponding to that of the primary current. This alternating'v induced earth potential is picked up by the potential electrodes 51 and 63 and is rectied by the reversing switch 52, which operates in synchronism with the first reversing switch 3l, to

produce a direct current through the leads 5,5 and 5i and the galvanometer 55.

A direct measuring potential, derived from the potentiometer 24, is applied to oppose the potential derived from the pick-up electrodes 51 and 0 63. The valuel of this measuring potential may be varied by adjusting the contacts 25 and -zs until the measuring potential exactly balances the picked-up potential as indicated by a null balance on the galvanometer 55. It is to be noted that this measuring potential is directly proportional to the current which is flowing in the earth current circuit, but that the potential circuit is not connected to the earth current circuit by a resistance connection which would form a direct current path. In this system there are no brushes or relay contacts in the secondary circuit which might introduce variations in resistance. In the embodiment of Fig.`2 the brushes 12 and 13 in the primary circuit do `not aect the accuracy oi the measurements inasmuch as the current flowing in the primary coil 3 constitutes the current ilowing in the earth circuit at any given instant or a predetermined portion thereof.

In making this measurement the effect of any residual earth current which would tend to produce a constant direct potential across the elec, trodes 51 and 53 is eliminated by suitable ad- .iustment oi' the potentiometer 50. This adjustment may be made, for example, while no current is owing through the earth circuit, so that the only effect on the galvanometer represents the effect of the residual earth current; It may also be made during operation of the sys.. -tem inasmuch as .the residual earth current, lwhichis a unidirectional currentyis reversed by the reversing switch 52 to produce an alternating current at the galvanometer 55, causing liuc-` tuation of the galvanometer. The adjustment of the contact 59 may accordingly be made to eliminate these uctuations of the galvanometer. -y

drift in the natural earth potential will be immediately perceivedfand can be compensated 'for by readjustmentof the potentiometer. Y

The setting of the potentiometer 24 measures the effective impedance of 'the earth to an electric current of the frequency at which the measurement'is being taken. The measurement is repeated 'at diierent low frequencies and in different parts of the area under investigation. 'I'he various` readings thus obtained may be interpreted to give an indication'of the characteristics of the area under investigation as set forth in the Evjen application above mentioned.

It is to be noted that the primary winding I of the coupling circuit A is connected on the alternating current side of the switch Il. causes Aperiodic reversal of the flux and prevents any permanent magnetizing effect from being built up in the core.

It is to be noted that the above described coupling circuit may be used to couple a secondary direct current circuit to a primary circuit carrying direct current or a low frequency alternating current and may be used for various measuring devices where a direct measuring potential having the characteristics above mentioned is required.

Although specific embodiments of the invention have been shown for purpose of illustration, it is to be understood that the invention is not to be restricted thereto, but that various changes and modifications may be made therein as will be readily apparent tiiA a person skilled in the art. The invention is only to be limited in accordance with the scope of the following claims.

What is claimed is:

1. A coupling circuit for coupling a primary circuit carrying direct current or low frequency alternating current to a D. C. secondary circuit for supplying to said secondary circuit a voltage drop proportional to the primary current for making precision measurements, said coupling circuit comprising a transformer having a magnetic circuit and primary and secondary windings coupled thereby, means connecting said primary winding to be energized from said primary circuit to produce a flux in said magnetic circuit proportional to said energization, means associated with said magnetic circuit to vary the reluctance thereof for eifecting corresponding changes in ilux, control means actuating said last means cyclically at a controlled frequency so as to produce an alternating current4 in the secondary Winding having a frequency determined by due to variations in speed of operation of saidy control means, so that the voltage drop supplied by said channel to said secondary circuit is unaiected-by changes in speed of operation. of said control means and is a function only of the current flowing in the primary circuit.

2. -A coupling -circuit for coupling a primary circuit carrying direct current or low frequency alternating current to a D. C. secondary circuit for supplying to said secondary circuit a voltage This 'ation of said flux and an amplitude varying as a function of the amplitude of the primary current and of the rate of variation of said flux, and a transmission channel connecting said secondary to supply a voltage drop to said secondary circuit. said channel including a filter network having frequency transmission characteristics to comv pensate for changes in current intensity in said secondary lwinding due to variations in speed of operation of said control means, so that the volt age drop supplied by said channel to said secondary circuit is unaffected by changes in speed of operation of said control means and is a function only of the current flowing in the primary 3. A coupling circuit for coupling a primary circuit carrying direct current or low frequency alternating current to a D. C. secondary circuit for supplying to said secondary circuit a voltage drop proportional to the primary current for making precision measurements, said coupling circuit comprising a transformer having a magnetic circuit including a rotatable segment forming a variable air gap and primary and secondary windings coupled thereby, means connecting said primary winding to be energized from said primary circuit to produce-a flux in Said magnetic circuit proportional vto said energization, control means rotating said'segment at a controlled frequency so as to produce an alternating current in the secondary winding having a frequency determined by the frequency of rotation of said segment and an amplitude varying as a function of the amplitude of the primary current and of the rate of variation of said flux, and a transmission channel connecting said secondary to supply a voltage drop to said secondary circuit, said channel including a filter network having frequency transmission characteristics to compensate for changes in current intensity in said secondary winding due to variations in speed of operation of said control means, so that the voltage drop supplied by said channel to said secondary circuit is unaffected by changes in speed of operation of said control means and is a function only of the current flowing in the primarycircuit.

4. A coupling circuit for coupling a. primary circuit carrying direct current or low frequency alternating current to a D. C. secondary circuit for supplying to said secondary circuit a voltage drop proportional to the primary current for making precision measurements, said coupling circuit comprising a transformer having a magnetic circuit and primary and secondary windings coupled thereby, means connecting said primary winding to be energized from said primary circuit to produce a nux in said magnetic circuit proportional to said energization, means associated with said magnetic circuit to vary the reluctance thereof for effecting corresponding changes in flux, control means actuating said last means drop proportional to the primary current for 76 cyqlically at a controlled frequency so as to pro ciuce an alternating current in the secondary tensity in said secondary winding due to variations in speed of operation of said control means, so that the current passed by said filter network is unaffected by changes in speed of operation of t said control means and is a function only of the current flowing in the primary circuit, a rectier connected to rectify the current passed by said network, a load resistance connected to pass the D. C.' output of said rectifier, and connections connecting said load resistance to supply a voltage drop to said secondary circuit.

5. In a geophysical prospecting system having an earth circuit carrying direct current or low frequency alternating current and 'a potential pick-up circuit influenced thereby, a coupling circuit for coupling said rst circuits for supplying to said potential circuit a potential drop proportional to the current owing in said earth current circuit for making precision measurements, said coupling circuit comprising a transformer having a magnetic circuit including a variable air gap end primary and secondary windings coupled thereby, means connecting said primary winding to be energized from said earth current to produce a flux in said magnetic circuit proportional to said energization, means associated with said magnetic circuit to vary the air gap for eiecting corresponding changes in ux, control means actuating said last means cyclically at a controlled frequency so as to produce an alternating current in the secondary winding having a frequency determined by the frequency of variation of said flux and an amplitude varying as a function of the amplitude of the primary current and of the rate of variation of said iiux, and a transmission channel connecting said secondary to supply a voltage drop to said potential pick-up circuit, said channel including a lter network 

